> > Hi,
> >
> > Anyone knocked up an accurate (at least 0.1%) mains frequency
measurement
> > device with a PIC? The basic requirement is to datalog the mains
> frequency
> > over a period of time as it can often be unstable.
>
> I have done this. (Unfortunately as a work-for-hire so I can't publish the
> code:-() It is relatively easy. You can just use the PICs crystal as a
> timebase, a zero cross detector with some hysteresis, and low-pass filter
> the result.
>
> * I had a go at this last year (with a 68HC11) and found that the zero
> cross detect was very slow and the cumulative time delay between detection
> of the pulse and being able to see it in the micro was not very
repeatable.
> I think it was maybe my bog-standard opto zero cross detect (slow) that
> scuppered it. It know it's pretty straight forward (especially with
> capture/compare) but getting that pulse in fast and with a known low delay
> seemed to be the problem....

Slow is not an issue. We are dealing with at least seconds here. What does
matter is consistency on the zero cross.

>
> > Reports of it being "speeded up" at the end of months to get the right
> > number of cycles in are often suggested.....(!)
>
> Actually, it is adjusted much more often than once a month.
>
> * I know - this was just one of the things "mentioned" to me when I
quizzed
> several people about the subject.
>
> Best regards,
> Dan

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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